A technique by which a transistor is formed using a semiconductor film formed over a substrate having an insulating surface has been attracting attention. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (also simply referred to as display device). As a semiconductor film applicable to the transistor, a silicon-based semiconductor material is widely known; moreover, a metal oxide exhibiting semiconductor characteristics (an oxide semiconductor) has been attracting attention as another material.
For example, Patent Document 1 discloses a technique in which a transistor is manufactured using an amorphous oxide containing In, Zn, Ga, Sn, and the like as an oxide semiconductor.
Although a transistor including an oxide semiconductor film can obtain transistor characteristics relatively with ease, the oxide semiconductor film is likely to be amorphous and has unstable physical properties. Thus, it is difficult to secure reliability of such a transistor.
On the other hand, there is a report that a transistor including a crystalline oxide semiconductor film has more excellent electrical characteristics and higher reliability than a transistor including an amorphous oxide semiconductor film (see Non-Patent Document 1).